Capacitor and inductor elements physically disposed in series whose lumped parameters are electrically connected in parallel to form a bandstop filter

ABSTRACT

One or more inductors and one or more capacitors are physically disposed relative to one another in series and are electrically connected to one another in parallel to form a bandstop filter. Chip inductors and chip capacitors having spaced apart conductive terminals are physically arranged in end-to-end abutting relation to minimize electrical potential between adjacent conductive terminals. The bandstop filter may be hermetically sealed within a biocompatible container for use with an implantable lead or electrode of a medical device. The values of the inductors and the capacitors are selected such that the bandstop filter is resonant at one or more selected frequencies, such as an MRI pulsed frequency.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.12/607,234, filed on Oct. 28, 2009, which is a continuation-in-part ofapplication Ser. No. 11/860,402, filed Sep. 24, 2007 now U.S. Pat. No.7,853,324 and a continuation-in-part of application Ser. No. 11/558,349,filed on Nov. 9, 2006 and which claims priority from U.S. provisionalapplication No. 61/109,672, filed on Oct. 30, 2008 and provisionalapplication No. 61/144,377, filed on Jan. 13, 2009.

FIELD OF INVENTION

The present invention relates to passive bandstop filter circuitswherein one or more of both inductor (L) and capacitor (C) elements arephysically disposed in series but whose equivalent (lumped) L-Cparameters are electrically connected in parallel. These novel L-Cbandstop filters may be wired in series or in parallel with the leads orcircuit traces of electronic circuits as needed for the particularapplication, for example, military, space, medical, commercialelectronics, aviation or other applications. More specifically, thepresent invention is particularly suitable for applications where it isimportant to keep the diameter or cross-sectional area of the bandstopfilter relatively small. A particular application of the invention isdirected to the bandstop filter being installed in series with medicalimplanted leads in order reduce the amount of radio frequency (RF)current and associated heating due to energy deposited on the leadsduring medical diagnostic procedures, such as magnetic resonance imaging(MRI). The bandstop filter is designed to be resonant at the MRI RFpulsed frequency and thereby present a high impedance in the lead thusreducing RF current flow. Reduction of MRI induced RF current in animplanted lead prevents dangerous overheating and the associatedpossibility of damage to adjacent tissues.

BACKGROUND OF THE INVENTION

This invention generally relates to the problem of energy induced intoimplanted leads during medical diagnostic procedures such as magneticresonant imaging (MRI). Specifically, the RF pulsed field of MRIequipment can couple to an implanted lead in such a way thatelectromagnetic forces (EMFs) are induced in the lead. The amount ofenergy that is induced is related to a number of complex factors, but ingeneral is dependent upon the local electric field that is tangent tolead and the integral of the electric field strength along the lead. Incertain situations, these EMFs can cause currents to flow into distalelectrodes or in the electrode interface with body tissue. It has beendocumented that when this current becomes excessive, overheating of saidelectrode or overheating of the associated interface with body tissuecan occur. There have been cases of damage to such body tissue which hasresulted in loss of capture of cardiac pacemaking pulses, tissue damagesevere enough to result in brain damage or multiple amputations, and thelike.

Implantable lead systems are generally associated with activeimplantable medical devices (AIMDs) such as cardiac pacemakers,cardioverter defibrillators, neurostimulators and the like. Implantableleads can also be associated with external devices such as externalpacemakers, externally worn neurostimulators (such as pain controlspinal cord stimulators) and the like.

Compatibility of cardiac pacemakers, implantable defibrillators andother types of active implantable medical devices with magneticresonance imaging (MRI) and other types of hospital diagnostic equipmenthas become a major issue. If one goes to the websites of the majorcardiac pacemaker manufacturers in the United States, which include St.Jude Medical, Medtronic and Boston Scientific (formerly Guidant), onewill see that the use of MRI is generally contra-indicated withpacemakers and implantable defibrillators.

However, an extensive review of the literature indicates that MRI isindeed often used with pacemaker, neurostimulator and other activeimplantable medical device (AIMD) patients. The safety and feasibilityof MRI in patients with cardiac pacemakers is an issue of gainingsignificance. The effects of MRI on patients' pacemaker systems haveonly been analyzed retrospectively in some case reports. There are anumber of papers that indicate that MRI on new generation pacemakers canbe conducted up to 0.5 Tesla (T). MRI is one of medicine's most valuablediagnostic tools. MRI is, of course, extensively used for imaging, butis also used for interventional medicine (surgery). In addition, MRI isused in real time to guide ablation catheters, neurostimulator tips,deep brain probes and the like. An absolute contra-indication forpacemaker patients means that pacemaker and implantable cardioverterdefibrillator (ICD) wearers are excluded from MRI. This is particularlytrue of scans of the thorax and abdominal areas. Because of MRI'sincredible value as a diagnostic tool for imaging organs and other bodytissues, many physicians simply take the risk and perform MRI on apacemaker patient. The literature indicates a number of precautions thatphysicians should take in this case, including limiting the power of theMRI RF pulsed field (Specific Absorption Rate—SAR level), programmingthe pacemaker to fixed or asynchronous pacing mode, and then carefulreprogramming and evaluation of the pacemaker and patient after theprocedure is complete. There have been reports of latent problems withcardiac pacemakers or other AIMDs after an MRI procedure sometimesoccurring many days later. Moreover, there are a number of recent papersthat indicate that the SAR level is not entirely predictive of theheating that would be found in implanted leadwires or devices. Forexample, for magnetic resonance imaging devices operating at the samemagnetic field strength and also at the same SAR level, considerablevariations have been found relative to heating of implanted leadwires.It is speculated that SAR level alone is not a good predictor of whetheror not an implanted device or its associated leadwire system willoverheat.

There are three types of electromagnetic fields produced by MRIequipment. The first type is the main static magnetic field designatedB₀ which is used to align protons in body tissue. The field strengthvaries from 0.5 to 3.0 Tesla in most of the currently available MRIunits in clinical use. Some of the newer MRI system fields can go ashigh as 4 to 5 Tesla. Certain research systems are as high as 11.7Tesla. This is over 100,000 times the magnetic field strength of theearth. A static magnetic field can induce powerful mechanical forces andtorque on any magnetic materials implanted within the patient. Thiswould include certain components within the cardiac pacemaker itselfand/or lead systems. It is not likely (other than sudden system shutdown) that the static MRI magnetic field can induce currents into thepacemaker lead system and hence into the pacemaker itself. It is a basicprinciple of physics that a magnetic field must either be time-varyingas it cuts across the conductor, or the conductor itself must movewithin the magnetic field for currents to be induced.

The second type of field produced by magnetic resonance imaging is thepulsed RF field, designated B₁, which is generated by the body coil orhead coil. This is used to change the energy state of the protons andelicit MRI signals from tissue. The RF field is homogeneous in thecentral region and has two main components: (1) the magnetic field iscircularly polarized in the actual plane; and (2) the electric field isrelated to the magnetic field by Maxwell's equations. In general, the RFfield is switched on and off during scanning protocols and usually has afrequency of 21 MHz to 64 MHz to 128 MHz depending upon the staticmagnetic field strength. The frequency of the RF pulse varies by theLamor equation with the field strength of the main static field where:RF PULSED FREQUENCY in MHz=(42.56) (STATIC FIELD STRENGTH IN TESLA).

The third type of MRI electromagnetic field is the time-varying magneticgradient fields designated G_(x), G_(Y), G_(z) which are used forspatial localization. These change their strength along differentorientations and operating frequencies on the order of 1 to 2 kHz. Thevectors of the magnetic field gradients in the x, y and z directions areproduced by three sets of orthogonally positioned coils and are switchedon only during the scanning protocols.

At very low frequency (VLF), voltages are induced at the input to thecardiac pacemaker as currents circulate throughout the patient's bodyand create voltage drops. Because of the vector displacement between thepacemaker housing and, for example, the Tip electrode, voltage dropacross the resistance of body tissues may be sensed due to Ohm's Law andthe circulating current of the RF signal. At higher frequencies, theimplanted lead systems actually act as antennas where voltages (EMFs)are induced along their length. These antennas are not very efficientdue to the damping effects of body tissue; however, this can often beoffset by extremely high power fields (such as MRI pulsed fields) and/orbody resonances. At very high frequencies (such as cellular telephonefrequencies), EMI signals are induced only into the first area of thelead system (for example, at the header block of a cardiac pacemaker).This has to do with the wavelength of the signals involved and wherethey couple efficiently into the system.

MRI gradient field coupling into an implanted lead system is based onloop areas and orientation. For example, in a cardiac pacemaker unipolarlead, there is a loop formed by the lead as it comes from the cardiacpacemaker housing to its distal tip, for example, located in the rightventricle. The return path is through body fluid and tissue generallyfrom the Tip electrode in the right ventricle back up to the pacemakercase or housing. This forms an enclosed area which can be measured frompatient X-rays in square centimeters. The average loop area is 200 to225 square centimeters. This is an average and is subject to greatstatistical variation. For example, in a large adult patient with anabdominal implant, the implanted loop area is much larger (approximately377 square centimeters). Relating now to the specific case of MRI, themagnetic gradient fields would be induced through enclosed loop areas.However, the pulsed RF fields, which are generated by the body coil,would be primarily induced into the lead system by antenna action.

At the frequencies of interest in MRI, RF energy can be absorbed andconverted to heat. The cause of heating in an MRI environment istwofold: (a) RF field coupling to the lead can occur which inducessignificant local heating; and (b) currents induced between the distaltip and tissue during MRI RF pulse transmission sequences can causelocal ohmic heating in tissue next to the distal Tip electrode of theimplanted lead. The power deposited by RF pulses during MRI is complexand is dependent upon the power (Specific Absorption Rate (SAR)) leveland duration of the RF pulse, the transmitted frequency, the number ofRF pulses applied per unit time, and the type of configuration of the RFtransmitter coil used. The amount of heating also depends upon thevolume of tissue imaged, the electrical resistivity of tissue and theconfiguration of the anatomical region imaged. There are also a numberof other variables that depend on the placement in the human body of theAIMD and its associated lead(s). For example, it will make a differencehow much EMF is induced into a pacemaker lead system as to whether it isa left or right pectoral implant. In addition, the routing of the leadand the lead length are also very critical as to the amount of inducedcurrent and heating that would occur. Also, distal Tip electrode designis very important as the distal Tip electrode itself can act as its ownantenna wherein eddy currents can create heating. The RF field of an MRIscanner can produce enough energy to induce lead RF voltages andresulting currents sufficient to destroy some of the adjacent myocardialtissue. Tissue ablation has also been observed. The effects of thisheating are not readily detectable by monitoring during the MRI scan.Indications that heating has occurred would include an increase inpacing threshold, venous ablation, Larynx or esophageal ablation,myocardial perforation and lead penetration, or even arrhythmias causedby scar tissue. However, these effects are typically determined sometime after the scan is completed. Such long term heating effects of MRIhave not been well studied yet for all types of AIMD lead geometries.There can also be localized heating problems associated with varioustypes of electrodes in addition to Tip electrodes. This includes Ringelectrodes or Pad electrodes. Ring electrodes are commonly used with awide variety of implanted devices including cardiac pacemakers,neurostimulators and the like. Pad electrodes are very common inneurostimulator applications. For example, spinal cord stimulators ordeep brain stimulators can include a plurality of Pad electrodes to makecontact with nerve tissue. A good example of this also occurs in acochlear implant. In a typical cochlear implant there would be sixteenRing electrodes placed up into the cochlea. Several of these Ringelectrodes make contact with auditory nerves.

Although there are a number of studies that have shown that MRI patientswith active implantable medical devices, such as cardiac pacemakers, canbe at risk for potential hazardous effects, there are a number ofreports in the literature that MRI can be safe for imaging of pacemakerpatients when a number of precautions are taken (only when an MRI isthought to be an absolute diagnostic necessity). While these anecdotalreports are of interest, they are certainly not scientificallyconvincing that all MRI can be safe. For example, just variations in thepacemaker lead length can significantly affect how much heat isgenerated. A paper entitled, HEATING AROUND INTRAVASCULAR GUIDEWIRES BYRESONATING RF WAVES by Konings, et al., Journal of Magnetic ResonanceImaging, Issue 12:79-85 (2000), does an excellent job of explaining howthe RF fields from MRI scanners can couple into implanted leads. Thepaper includes both a theoretical approach and actual temperaturemeasurements. In a worst-case, they measured temperature rises of up to74 degrees C. after 30 seconds of scanning exposure. The contents ofthis paper are incorporated herein by reference.

The effect of an MRI system on the function of pacemakers, ICDs,neurostimulators and the like, depends on various factors, including thestrength of the static magnetic field, the pulse sequence, the strengthof RF field, the anatomic region being imaged, and many other factors.Further complicating this is the fact that each patient's condition andphysiology is different and each manufacturer's pacemaker and ICDdesigns also are designed and behave differently. Most experts stillconclude that MRI for the pacemaker patient should not be consideredsafe.

It is well known that many of the undesirable effects in an implantedlead system from MRI and other medical diagnostic procedures are relatedto undesirable induced EMFs in the lead system and/or RF currents in itsdistal Tip (or Ring) electrodes. This can lead to overheating of bodytissue at or adjacent to the distal Tip electrode.

Distal Tip electrodes can be unipolar, bipolar and the like. It is veryimportant that excessive current not flow at the interface between thedistal Tip electrode and body tissue. In a typical cardiac pacemaker,for example, the distal Tip electrode can be passive or of a screw-inhelix type. In any event, it is very important that excessive RF currentnot flow at this junction between the distal Tip electrode and forexample, myocardial or nerve tissue. This is because tissue damage inthis area can raise the capture threshold or completely cause loss ofcapture. For pacemaker dependent patients, this would mean that thepacemaker would no longer be able to pace the heart. This would, ofcourse, be life threatening for a pacemaker dependent patient. Forneurostimulator patients, such as deep brain stimulator patients, theability to have an MRI is equally important.

The most important and most life-threatening item is to be able tocontrol overheating of implanted leads during an MRI procedure. A noveland very effective approach to this is to install parallel resonantinductor and capacitor bandstop filters at or near the distal electrodeof implanted leads, as described in U.S. Pat. No. 7,363,090, and U.S.Patent Publication Nos. US 2007/0112398 A1; US 2008/0071313 A1; US2008/0049376 A1; US 2008/0161886 A1; US 2008/0132987 A1; US 2008/0116997A1; and US 2009/0163980 A1 the contents all of which are incorporatedherein. US 2007/0112398 A1 relates generally to L-C bandstop filterassemblies, particularly of the type used in active implantable medicaldevices (AIMDs) such as cardiac pacemakers, cardioverter defibrillators,neurostimulators and the like, which raise the impedance of internalelectronic or related wiring components of the medical device atselected frequencies in order to reduce or eliminate currents inducedfrom undesirable electromagnetic interference (EMI) signals.

U.S. Pat. No. 7,363,090 and US 2007/0112398 A1 disclose resonant L-Cbandstop filters to be placed at the distal tip and/or at variouslocations along the medical device leadwires or circuits. These bandstopfilters inhibit or prevent current from circulating at selectedfrequencies of the medical therapeutic device. For example, for an MRIsystem operating at 1.5 Tesla, the pulsed RF frequency is 63.8 MHz, asshown by the Lamour Equation. The bandstop filter can be designed toresonate at or near 64 MHz and thus create a high impedance (ideally anopen circuit) in the lead system at that selected frequency. Forexample, the bandstop filter, when placed at the distal tip of apacemaker leadwire, will significantly reduce RF currents from flowingthrough the distal tip and into body tissue. It will be obvious to thoseskilled in the art that all of the embodiments described in U.S. Pat.No. 7,363,090 are equally applicable to a wide range of otherimplantable and external medical devices, including deep brainstimulators, spinal cord stimulators, drug pumps, probes, catheters andthe like.

Electrically engineering a capacitor in parallel with an inductor isknown as a tank circuit or bandstop filter. It is well known that when anear-ideal bandstop filter is at its resonant frequency, it will presenta very high impedance. Since MRI equipment produces very large RF pulsedfields operating at discrete frequencies, this is an ideal situation fora specific resonant bandstop filter. Bandstop filters are more efficientfor eliminating one single frequency than broadband filters. Because thebandstop filter is targeted at this one frequency, it can be muchsmaller and volumetrically efficient.

However, a major challenge when designing a bandstop filter for humanimplant is that it must be very small in size, biocompatible, and highlyreliable. Coaxial geometry is preferred. The reason that a coaxialgeometry is preferred is that leads are placed at locations in the humanbody primarily by one of two main methods. The first is guide wireendocardial lead insertion. For example, in a cardiac pacemakerapplication, a pectoral pocket is created and then the physician makes asmall incision and accesses the cephalic or subclavian vein. Theendocardial pacemaker leads are stylus guided/routed down through thisvenous system through the right atrium, through the tricuspid valve andinto, for example, the right ventricle. A second primary method ofinstalling leads (particularly for neurostimulators) in the human bodyis by tunneling. In tunneling, a surgeon uses special tools to tunnelunder the skin and through the muscle, for example, up through the neckto access the Vagus nerve or the deep brain. In both techniques, it isvery important that the leads and their associated electrodes at thedistal tips be very small.

Accordingly, there is a need for a bandstop filter for medical devices,and particularly human implanted devices and components thereof, whichis very small in size, biocompatible, and highly reliable. There is alsoa need for such a bandstop filter which can be placed coaxially relativeto a leadwire or electrode of a lead system. The present inventionfulfills these needs, and provides other related advantages.

SUMMARY OF THE INVENTION

The present invention relates to passive bandstop filter circuitswherein one or more of both inductor (L) and capacitor (C) elements arephysically disposed in series but whose equivalent (lumped) LCparameters are electrically connected in parallel. More particularly,the bandstop filter comprises an inductor having first and secondconductive terminals in spaced non-conductive relation, and a capacitorhaving first and second conductive terminals in spaced non-conductiverelation, wherein the inductor and the capacitor are physically disposedin series relative to one another, and wherein the inductor and thecapacitor are electrically connected to one another in parallel.

In the illustrated embodiments, one of the first or second conductiveterminals of the inductor is disposed generally adjacent to one of thefirst or second conductive terminals of the capacitor. Such anarrangement results in the capacitor and the inductor being alignedalong a common axis. In preferred embodiments, the adjacent conductiveterminals of the inductor and the capacitor abut one another. However,if the electrical potential of the adjacent surfaces has not beenminimized or zeroed, an electrical insulator may be disposed between theadjacent conductive terminals of the inductor and the capacitor.

As illustrated herein, the inductor comprises a chip inductor, and thecapacitor comprises a chip capacitor. The second conductive terminal ofthe inductor is preferably conductively coupled to the first conductiveterminal of the capacitor, and the first conductive terminal of theinductor is conductively coupled to the second conductive terminal ofthe capacitor, all the while the inductor and the capacitor beingphysically disposed in series relative to one another.

The parallel capacitor and inductor may be disposed in series in anelectrical lead or circuit trace. The capacitor and the inductor may betuned to impede induced current flow through the electrical lead at aselected frequency. Typically, the electrical lead comprises a portionof an implanted lead for a medical device. The electrical lead mayinclude an active fixation tip, wherein the bandstop filter is disposedwithin the active fixation tip.

The bandstop filter may further comprise a plurality of paired inductorsand capacitors, wherein in each paired inductor and capacitor, theinductor and the capacitor are physically disposed in series relative toone another and yet electrically connected to one another in parallel.Each paired inductor and capacitor may further be electrically connectedin series to another paired inductor and capacitor.

In another embodiment, the parallel capacitor and inductor are disposedin parallel between two electrical leads or circuit traces. Thecapacitor and the inductor are tuned to divert induced current flowthrough the electrical leads except at a selected frequency.

The capacitor and the inductor may be comprised of biocompatible andnon-migratable materials. In particular, the inductor, the capacitor,and all associated electrical connections, and support substrates, ifany, may comprise biocompatible materials to form a biocompatiblepackage suitable for mammalian implantation. However, when elements ofthe capacitor and/or the inductor comprise non-biocompatible materials,they may be disposed within a hermetically sealed container. In thiscase, the hermetically sealed container comprises a biocompatiblehousing in which the bandstop filter is disposed, and biocompatiblefirst and second conductive contacts extending through the housing whichare conductively coupled in series to the bandstop filter. In medicalimplant applications, the hermetically sealed container may be disposedin series in the electrical lead, and the first and second contacts maybe connected to, respectively, first and second portions of the lead. Ina related assembly process, a substrate is provided onto which theinductor and the capacitor are fixed in a pre-assembly prior toinsertion into the biocompatible housing. The pre-assembly is testedprior to insertion into the biocompatible housing, and after thepre-assembly is inserted into the biocompatible housing, hermeticalterminals comprising at least a portion of the first and secondconductive contacts are hermetically sealed to the housing.

In several of the illustrated embodiments, the inductor comprises aplurality of inductors which may be conductively coupled to one anothereither in series or in parallel. However, in accordance with the presentinvention, the plurality of inductors are physically disposed in seriesrelative to one another. In a similar manner, the capacitor may comprisea plurality of capacitors conductively coupled to one another either inseries or in parallel. Again, in accordance with the present invention,the plurality of capacitors is physically disposed in series relative toone another.

The values of the inductor and the capacitor are selected such that thebandstop filter is resonant at a selected frequency. The overall Q ofthe bandstop filter is selected to balance impedance at the selectedfrequency versus frequency bandwidth characteristics. This may beaccomplished when the Q of the inductor is relatively high and the Q ofthe capacitor is relatively low, such as when the inductor has arelatively low resistive loss and when the capacitor has a relativelyhigh equivalent series resistance. Alternatively, this may also beaccomplished when the Q of the inductor is relatively low and the Q ofthe capacitor is relatively high, which is accomplished when theinductor has a relatively high resistive loss and the capacitor has arelatively low equivalent series resistance. The selected frequency maycomprise an MRI pulsed frequency, and the overall Q of the bandstopfilter may be selected to attenuate current flow along a lead or circuittrace through a range of selected frequencies.

The inductor and the capacitor may be mounted on a flexible substrate,which itself may include portions that are wrapped around the capacitorand the inductor during the assembly process. Typically, such a wrappedassembly is disposed within a protective container such as ahermetically sealed biocompatible housing.

In an illustrated embodiment, the inductor is disposed on a firstsurface of an intermediate substrate, and the capacitor is disposed on asecond generally opposite surface of the intermediate substrate. Circuittraces extend through the intermediate substrate and conductively couplethe inductor and the capacitor in parallel. Of course, all of theaforementioned assemblies may be formed utilizing robotic manufacturingtechniques wherein the inductor and the capacitor are roboticallydeposited on the substrate. The substrate itself may comprise amulti-layered flex cable

Finally, in yet another illustrated embodiment, the capacitor comprisesa feedthrough capacitor and the inductor comprises a chip inductor. Inaccordance with the present invention, the chip inductor and thefeedthrough capacitor are physically disposed in series but theequivalent (lumped) LC parameters are electrically connected in parallelto form a bandstop filter. The chip inductor and the feedthroughcapacitor may be disposed within a biocompatible housing; however, incomparison with other embodiments, only a single hermetic seal assemblyis required thus reducing costs.

All of the illustrated embodiments are suitable for use withultra-miniature inductor and capacitor chip components that aremechanically installed in hermetic packages in series, but haveelectrical circuit traces that put the components electrically inparallel, to form the desired bandstop filter having tank circuitcharacteristics.

Other features and advantages of the present invention will becomeapparent from the following more detailed description, taken inconjunction with the accompanying drawings, which illustrate, by way ofexample, the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate the invention. In such drawings:

FIG. 1 is a wire-formed diagram of a generic human body showing a numberof exemplary medical devices.

FIG. 2 is an elevational view of a typical prior art cardiac pacemakershowing the metal case and an IS-1 header block.

FIG. 3 is a perspective view of the cardiac pacemaker of FIG. 2, withexemplary associated leads to the heart.

FIG. 4 is a schematic illustration of a bipolar leadwire system with adistal Tip and ring typically as used with a cardiac pacemaker.

FIG. 5 is a schematic illustration of a prior art single chamber bipolarcardiac pacemaker lead showing the distal Tip and the distal Ringelectrodes.

FIG. 6 is an enlarged, fragmented schematic view taken generally alongthe line 6-6 of FIG. 5, illustrating placement of bandstop filtersadjacent to the distal tip and Ring electrodes.

FIG. 7 is a cross-sectional view of a generic prior art active fixationdistal tip typically used in conjunction with cardiac pacemakers.

FIG. 8 is a schematic diagram of a distal Tip electrode tank circuit orbandstop filter.

FIG. 9 is a graph showing impedance versus frequency for the paralleltank circuit of FIG. 8.

FIG. 10 is a schematic illustration of a unipolar AIMD lead system witha bandstop filter disposed near the distal electrode.

FIG. 11 is a graph of attenuation versus frequency for capacitors havinghigh, medium and low Q.

FIG. 12 is a schematic illustration of a bipolar AIMD wherein multiplebandstop filters are disposed in series with each one of the leads.

FIG. 13 is a schematic illustration of bipolar AIMD leads wherein abandstop filter is disposed between the leads to form a divertercircuit.

FIG. 14 is a perspective view of a hermetically sealed L-C bandstopfilter assembly embodying the present invention.

FIG. 15 is an illustration of how small the hermetically sealed assemblyof FIG. 14 is in comparison with a U.S. one-cent coin.

FIG. 16 is a cross-sectional view taken generally along the line 16-16from FIG. 14.

FIG. 17 is a perspective view of a hermetic terminal shown in FIGS. 14and 16.

FIG. 18 is a sectional view of the hermetic terminal taken generallyalong the line 18-18 from FIG. 16.

FIG. 19 is an elevational view taken generally along the line 19-19 fromFIG. 16.

FIG. 20 is a perspective view illustrating a multilayer flex cable ontowhich a chip capacitor and a chip inductor are mounted in accordancewith the present invention.

FIG. 21 is an electrical/physical schematic of the bandstop filterassembly of FIGS. 16 and 20, illustrating non-preferred conductivepathways and electrical connections to the serially arranged capacitorand inductor.

FIG. 22 is a purely electrical schematic of the bandstop filter of FIGS.16 and 20.

FIG. 23 is a perspective view of an alternative construction of thebandstop filter wherein the chip inductor and chip capacitor are mountedon a flexible circuit substrate.

FIG. 24 is a perspective view of the assembly of FIG. 23, wherein thecircuit substrate is folded up for insertion into a protective housingor container.

FIG. 25 is a top plan view of another alternative embodiment, whereinthe serial inductor and capacitor are electrically connected in parallelin accordance with the non-preferred method shown in FIG. 21, andwherein an electrical insulator is disposed between adjacent ends of theinductor and the capacitor.

FIG. 26 illustrates yet another embodiment, wherein the serial capacitorand inductor are situated on opposite sides of an intermediatesubstrate.

FIG. 27 is an exploded perspective view of the bandstop filter assemblyof FIGS. 16 and 20, illustrating a preferred arrangement forelectrically connecting the inductor and capacitor in parallel whilethey are physically arranged in series.

FIG. 28 is an electrical/physical schematic similar to FIG. 21,illustrating preferred conductor pathways and electrical connections tothe serially arranged capacitor and inductor shown in FIG. 27.

FIG. 29 illustrates another embodiment where two bandstop filters areplaced in series with one another within a hermetically sealedcontainer.

FIG. 30 is a purely electrical schematic of the dual bandstop filterassembly of FIG. 29.

FIG. 31 is an electrical/physical schematic similar to FIGS. 21 and 28,illustrating preferred conductive pathways and electrical connectionsfor the dual bandstop filter assembly of FIGS. 29 and 30.

FIG. 32 is a perspective sectional view illustrating yet anotherembodiment where three inductors are physically placed in series with asingle capacitor and yet electrically connected to the capacitor inparallel.

FIG. 33 is an electrical/physical schematic diagram of the connectionsbetween the inductors and the capacitors of FIG. 32.

FIG. 34 is a purely electrical schematic of the assembly of FIGS. 32 and33.

FIG. 35 is an exploded perspective view of the assembly of FIG. 32.

FIG. 36 is an electrical/physical schematic diagram similar to FIG. 33,but illustrating three inductors and a single capacitor all electricallyconducted in parallel.

FIG. 37 is a purely electrical schematic of the assembly of FIG. 36.

FIG. 38 is an electrical/physical schematic diagram similar to FIGS. 33and 36, but illustrating two capacitors and a single inductor allelectrically connected in parallel.

FIG. 39 are equivalent electrical schematics for the assembly of FIG.38.

FIG. 40 is an electrical/physical schematic diagram similar to FIG. 38,but illustrating two capacitors electrically connected in series, andthen collectively electrically connected in parallel with a singleinductor.

FIG. 41 are equivalent electrical schematics for the assembly of FIG.40.

FIG. 42 is a fragmented perspective view of a passive electrodetypically used in cardiac pacemaker applications.

FIG. 43 is a fragmented perspective view of an active fixation tip.

FIG. 44 is an enlarged, fragmented sectional view taken generally alongthe line 44-44 from FIG. 43, illustrating placement of a bandstop filterin accordance with the present invention in series with an electricallead for a medical device.

FIG. 45 illustrates another embodiment where a chip inductor and afeedthrough capacitor are placed in series within a hermetically sealedcontainer.

FIG. 46 is an electrical/physical schematic similar to FIGS. 21 and 28,illustrating conductive pathways and electrical connections for thebandstop filter assembly of FIG. 45.

FIG. 47 is a purely electrical schematic of the bandstop filter assemblyof FIGS. 45 and 46.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown in the accompanying drawings for purposes of illustration, thepresent invention is directed to miniature inductor and chip componentswhich are physically arranged in series, but electrically connected toone another in parallel to form tank circuits and bandstop filters forimpeding or diverting currents induced by electromagnetic interference,for example, in a lead or an electrode of a medical device. Suchbandstop filters may be placed electrically in series with an implantedlead or electrode of an active implantable medical device (AIMD), and ina variety of other electronics circuits used in commercial electronics,military, aerospace or other applications, where it may serve as animpeder at certain resonant frequencies. The bandstop filter of thepresent invention may also be placed electrically in parallel betweenleads or circuit traces where it may serve as a RF current diverter atthe resonant frequency.

FIG. 1 is a wire formed diagram of a generic human body showing a numberof active implantable and external medical devices 100 that arecurrently in use. 100A represents a family of hearing devices which caninclude the group of cochlear implants, piezoelectric sound bridgetransducers and the like. 100B represents a variety of neurostimulatorsand brain stimulators. Neurostimulators are used to stimulate the Vagusnerve, for example, to treat epilepsy, obesity and depression. Brainstimulators are pacemaker-like devices and include electrodes implanteddeep into the brain for sensing the onset of the seizure and alsoproviding electrical stimulation to brain tissue to prevent the seizurefrom actually occurring. The leads associated with a deep brainstimulator are often placed using real time MRI imaging. Most commonlysuch leads are placed during real time MRI. 100C shows a cardiacpacemaker which is well-known in the art. 100D includes the family ofleft ventricular assist devices (LVAD's), and artificial hearts,including the recently introduced artificial heart known as the Abiocor.100E includes an entire family of drug pumps which can be used fordispensing of insulin, chemotherapy drugs, pain medications and thelike. Insulin pumps are evolving from passive devices to ones that havesensors and closed loop systems. That is, real time monitoring of bloodsugar levels will occur. These devices tend to be more sensitive to EMIthan passive pumps that have no sense circuitry or externally implantedleadwires. 100F includes a variety of bone growth stimulators for rapidhealing of fractures. 100G includes urinary incontinence devices. 100Hincludes the family of pain relief spinal cord stimulators andanti-tremor stimulators. 100H also includes an entire family of othertypes of neurostimulators used to block pain. 100I includes a family ofimplantable cardioverter defibrillators (ICD) devices and also includesthe family of congestive heart failure devices (CHF). This is also knownin the art as cardio resynchronization therapy devices, otherwise knownas CRT devices. 100J illustrates an externally worn pack. This packcould be an external insulin pump, an external drug pump, an externalneurostimulator or even a ventricular assist device. 100K illustratesthe insertion of an external probe or catheter. These probes can beinserted into the femoral artery, for example, or in any other number oflocations in the human body. 100L illustrates one of various types ofEKG/ECG external skin electrodes which can be placed at variouslocations. 100M are external EEG electrodes placed on the head.

FIGS. 2 and 3 are drawings of a typical cardiac pacemaker 100C showing atitanium case or housing 102 and an IS-1 header connector block 104. Thetitanium case or housing 102 is hermetically sealed, however there is apoint where leadwires 106 must ingress and egress a hermetic seal. Thisis accomplished by providing a hermetic terminal assembly 108 thatgenerally consists of a ferrule 110 which is laser welded to thetitanium housing 102 of the AIMD 100C.

Referring to FIG. 3, four leadwires are shown consisting of leadwirepair 106 a and 106 b and leadwire pair 106 c and 106 d. This is typicalof what is known as a dual chamber bipolar cardiac pacemaker. The IS-1connectors 112 and 112′ of leads 114 and 114′ are designed to plug intoreceptacles 116 and 116′ in the header block 104. The receptacles 116and 116′ are low voltage (pacemaker) connectors covered by an ANSI/AAMIISO standard IS-1. Higher voltage devices, such as implantablecardioverter defibrillators (ICDs), are covered by ANSI/AAMI ISOstandard DF-1. A new standard which will integrate both high voltage andlow voltage connectors into a miniature in-line quadripolar connector isknown as the IS-4 series. The implanted leads 114 and 114′ are typicallyrouted in a pacemaker application down into the right atrium 118 and theright ventricle 118′ of the heart 120. New generation biventriculardevices may introduce leads to the outside of the left ventricle, whichdevices have proven to be very effective in cardiac resynchronizationand treating congestive heart failure (CHF).

An RF telemetry pin antenna 122 is also shown which is not electricallyconnected to the leadwires 106 or the receptacles 116. The RF telemetrypin antenna 122 acts as a short stub antenna for picking up telemetry(programming) signals that are transmitted from the outside of thedevice 100C.

Although the present invention will be described herein in the contextand environment of a cardiac pacemaker 100C and its associated leads114, the present invention may also be advantageously utilized in manyother types of AIMDs as briefly outlined above, as well as in othercommercial electronic, military, aerospace and other applications. Inthe following discussion, to the extent practicable, functionallyequivalent components will retain the same or a similar (in incrementsof 100) reference number, irrespective of the particular embodimentbeing described.

FIG. 4 illustrates a prior art single chamber bipolar device 100C andlead system 114 and 114′ with a distal Tip electrode 124 and a Ringelectrode 126 typically as used with the cardiac pacemaker 100C. Shouldthe patient be exposed to the fields of an MRI scanner or other powerfulemitter used during a medical diagnostic procedure, currents that aredirectly induced in the lead system 114 can cause heating by I²R lossesin the lead system or by heating caused by RF current flowing from theTip and Ring electrodes 124, 126 into body tissue. If these induced RFcurrents become excessive, the associated heating can cause damage oreven destructive ablation to body tissue.

FIG. 5 illustrates a single chamber bipolar cardiac pacemaker 100C, andleads 114 and 114′ having distal Tip 124 and distal Ring 126 electrodes.This is a spiral wound (coaxial) system where the Ring coil 114′ iswrapped around the Tip coil 114. There are other types of pacemakerleadwire systems in which these two leads lay parallel to one another(known as a bifilar lead system), which are not shown.

FIG. 6 is an enlarged schematic illustration of the area “6-6” in FIG.5. In the area of the distal Tip 124 and Ring 126 electrodes, bandstopfilters 128 and 128′ have been placed in series with each of therespective Ring and Tip circuits. The Ring circuit wire 114′ has beendrawn straight instead of coiled for simplicity. The bandstop filters128 and 128′ are tuned such that, at an MRI pulsed RF frequency, a highimpedance will be presented thereby reducing or stopping the flow ofundesirable MRI induced RF current from the electrodes 124 and 126 intobody tissues.

The Tip electrode 124 is designed to be inserted into intimate contactwith myocardial tissue. Over time it becomes encapsulated and fullyembedded or buried within such tissue. However, the Ring electrode 126is designed to float within the blood pool, for example, in theventricle 118′ or atrium 118. With the constant blood perfusion, theRing electrode 126 is somewhat cooled during medical diagnosticprocedures, such as MRI. However, the Tip electrode 124, which isembedded in the myocardial tissue, is thermally insulated in comparison.Moreover, it can't always be assumed that a Ring electrode 126 that isfloating in the blood pool will be adequately cooled by the flow ofblood. There are certain types of patients that have cardiovasculardiseases that lead to very low blood flow rates and perfusion issues.The Ring electrode 126 can also become encapsulated by body tissues.Accordingly, both the distal Tip electrode 124 and the Ring electrode126 are preferably both associated with bandstop filters 128 and 128′.However, since the operation of the bandstop filter 128 is moreimportant with the Tip electrode 124 than it is with the Ring electrode126 in order to prevent distal tip heating and associated tissue damage,in many cardiac applications only a Tip bandstop filter 128 may berequired for MRI compatibility.

FIG. 7 is a cross-sectional view of a generic prior art active fixationdistal tip 130 which is typically used in conjunction with cardiacpacemakers. There is a metallic housing 132 which contains a sharptipped distal helix coil 134. This helix coil 134 is shown in itsretracted position, which enables the physician to insert the fixationtip assembly 130 endocardially through the venous system, through theatrium, and through the tricuspid valve into the right ventricle so itdoes not snag or tear any tissue, and is designed to be extended andscrewed into myocardial tissue. Once it is in the appropriate position,the physician then turns leadwire spline assembly 136 in a clockwiserotation. This is done outside the pectoral pocket with the lead 114protruding from the body. A torque tool is generally applied so that thephysician can twist or screw the helix coil 134 into place. Protrusion138 acts as a gear so that as helix coil 134 is turned, it is screwedforward. This makes for a very reliable fixation into myocardial tissue.The helix coil 134 is generally attached by a laser weld 140 to an endof the spline assembly 136 as shown. Attached to spline assembly 136,usually by laser welding, is the lead 114 coming from the AIMD. Anoptional feature 142 is placed on spline assembly 136 to create apositive stop as the physician is turning the leadwire assembly andscrewing the helix coil 134 into body tissue. Of course, all of thematerials of the active fixation tip 130 shown in FIG. 7 arebiocompatible. Typically, the helix coil 134 is made of platinum iridiumalloy and would be coated with various materials to improve electricalperformance. The housing 132 would generally be composed of titanium oranother equivalent biocompatible alloy. The spline 136 is generally aplatinum iridium alloy.

FIG. 8 is the schematic diagram of a distal tip bandstop filter circuit128 that can be inserted in series generally in location 144 in FIG. 7,as described in US 2007/0112398 A1. In order to do this, it is usuallyimportant that the inductor element L 146(L) and the capacitor element148(C) be hermetically enclosed and also mechanically protected.Accordingly, they are typically installed in a hermetically sealedmechanically robust enclosure. However, these components must be verysmall in diameter to keep the lead and its associated distal tip smallenough for insertion into various body tissues.

FIG. 9 is a graph showing impedance versus frequency for the idealparallel bandstop filter circuit 128 of FIG. 8. As one can see, usingideal (zero resistance) circuit components, the impedance measuredbetween the lead 114 and the helix coil 134 is zero until one approachesthe resonant frequency f_(r). At the frequency of resonance, these idealcomponents (the parallel inductor 146 and capacitor 148) combinetogether to approach an infinite impedance.

FIG. 10 is a drawing of a generic unipolar AIMD 100 and lead 114, withthe bandstop filter 128 added at or near the distal electrode 134. Theinductor 146 has a resistance element R_(L) in series with it. Thecapacitor 148 also has a resistance R_(C) in series with it. Theresistances R_(L) and R_(C) can be separate discrete resistors or theyare losses of the inductor and capacitor elements themselves. Ingeneral, the resistance R_(L) will be the resistance of the circuittraces or wires used to form the inductor 146. The capacitor 148 hasohmic losses R_(C) due to the resistance of its internal electrodeplates, connection to its electrode plates, and dielectric losses. Inthe capacitor industry this is known as the capacitor's equivalentseries resistance or ESR. The bandstop filter circuit 128 illustrated inFIG. 10 is a “real” bandstop filter in that the resistive losses areincluded. This makes it distinct from the ideal bandstop filter circuit128 shown in FIG. 8. The presence of the bandstop filter 128 willpresent a very high impedance at a specific MRI RF pulse frequency toprevent currents from circulating through the distal electrode 134 intobody tissue at this specific frequency.

FIG. 11 is a family of curves 150, 152 and 154 which show theattenuation in dB versus frequency for the bandstop filters 128 of thepresent invention. Curve 150 represents the use of very high Q inductorand capacitor components. If the capacitor and the inductor were ideal,meaning that they would both have zero resistance, then there would beno 3 db bandwidth at all between points “a” and “b”. However, since inthe real world both the inductor and the capacitor do have losses, a 3db bandwidth separation between points “a” and “b” is achieved. It isvery important that there be suitable bandwidth for two reasons: one,the MRI machine has gradient fields which change the RF frequency. Thisis how the MRI machine selects a slice to image, for example, throughthe knee. It does this by modifying the 1.5 Tesla or main static fieldby using a gradient field. This causes the Lamor frequency to change.Accordingly, one can see that some bandwidth is required centered aroundthe specified pulsed resonant frequency of the MRI equipment so that allof these frequencies are properly attenuated in an implanted lead. Ifone were to deliberately use an inductor with a very high DC resistanceand a capacitor with very high ESR, this would result in very low Qcomponents and the resulting attenuation curve 152. The low Qattenuation curve 152 attenuates over a very broad range of frequencies;however, the attenuation in dB has been sacrificed.

Attenuation curves 154 or 156 shown in FIG. 11 are generally preferred.One can do this by controlling the relative Q of the inductor and thecapacitor components of the bandstop filter 128. In one embodiment, theQ of the inductor would be relatively low and the Q of the capacitorwould be relatively high. This means that the inductor would have arelatively high internal resistance and the capacitor would have arelatively low equivalent series resistance. This is achieved by usingmultiple turns of relatively small wire to create a high DC resistancein the inductor, and by using multiple and robust electrode plates tokeep the equivalent series resistance (ESR) of the capacitor relativelylow. The overall Q of the bandstop filter is thus selected to balanceimpedance at the selected frequency versus frequency bandwidthcharacteristics. The values of the inductor and the capacitor selectedare such that the bandstop filter 128 is resonant at a selectedfrequency, and preferably selected to attenuate current flow through thelead or electrode along a range of selected frequencies. Such afrequency or range of frequency may include an MRI pulsed frequency.Typically, the Q of the inductor is relatively low or moderate, and theQ of the capacitor is relatively high or moderate to select the overallQ of the bandstop filter. That is, the inductor has a relatively highresistive loss R_(L), and the capacitor has a relatively low equivalentseries resistance R_(C).

FIG. 12 illustrates a generic bipolar AIMD 100, meaning that it has twoimplanted leads 114 and 114′. Shown are multiple bandstop filters 128,128′ in series with each one of the leads 114 and 114′. For example,lead 114 has two bandstop filters 128 connected in series. As mentionedin US 2007/0112398 A1, these could be designed to resonate at twodifferent frequencies, thereby providing attenuation to the RF pulsefields of both 1.5 Tesla and 3 Tesla MRI scanners. For example, theindividual bandstop filters 128 in lead 114 could be designed to beresonant at 64 MHz (Fr₁) and 128 MH_(z) (Fr₂), respectively. This wouldhave the desired effect of having a high impedance at both of thesecommon MRI RF pulsed frequencies thereby providing a high level ofattenuation to RF induced currents at both 1.5 and 3.0 T. There couldalso be additional bandstop filters 128 if needed.

FIG. 13 shows two circuit traces or leads 114 and 114′, and the novelbandstop filter 128 of the present invention wired in parallel betweenthe circuit traces or leads 114 and 114′. When the bandstop filter 128is wired in parallel, instead of in series as shown FIGS. 6, 8, 10 and12, the bandstop filter 128 becomes an RF current diverter instead of anRF current impeder. In FIG. 13, RF frequencies that form a voltagepotential between circuit traces or leads 114 and 114′ will all bediverted except at one frequency which is the resonant frequency of thebandstop filter 128. These types of circuits have broad utility in manytypes of radio applications or receiver applications, and many othertypes of electronic circuits used in the military, aerospace, andcommercial markets.

As mentioned above, for medical implant applications it is veryimportant that the implanted leads and their associated electrodes atthe distal tips be very small. It is particularly important that thecross-sections or diameters of the bandstop filters be very small foreasy endocardial insertion into the venous system of the human body. Thepresent invention meets these criteria by using a novel combination ofcomponents that are mechanically mounted in series, but whose lumpedelements are electrically in parallel. The components generally consistof commercial off-the-shelf miniature chip capacitor and inductorcomponents. These are generally manufactured in high volume throughoutthe world. Accordingly, they are very inexpensive, but more importantly,they are very small in size. By way of example, a few years ago a smallsized monolithic chip capacitor (MLCC) would be 0603, meaning that itwould be 0.060 inch long by 0.030 inch in width. In comparison, todayinductor and capacitor chip components can be purchased as small as 0201or 01005. This means that they are so small that they literally can fitthrough a pepper shaker. Human hands cannot possibly handle componentsthis small. Accordingly, micro-robotic manufacturing is the preferredmethod of manufacturing the novel components assemblies of the presentinvention, wherein the components typically are delivered on tape andreel and fed into the robots which pick and place the components andthen go through a series of steps including additional componentplacement, wave soldering, cleaning, automatic optical inspection andautomated electrical testing. All of this is done in a linear roboticmanufacturing operation that is completely or nearly free of humanhands. In cardiac rhythm applications (pacemakers and ICDs), a desirablelead size is 6 French (0.079 inches in diameter). For deep brainstimulator applications, an even smaller size is desirable, such as 3French, which is 1 millimeter in diameter or 0.039 inches. US2007/0112398 A1 discloses a number of methods of manufacturing novelbandstop filters for placement in the lead systems of active implantablemedical devices. The present invention extends these concepts further.

In mammalian implant applications, the bandstop filters of the presentinvention should be small and placed in series with the implanted leador electrode of the medical device. In such applications, it isnecessary that the bandstop filter itself or a container therefor bebiocompatible and highly reliable. Although commercial off-the-shelfcapacitor and inductor components are very small in size, arranging themsuch that they are electrically coupled and likewise physically placedin parallel can increase the size of the bandstop filter wherecomplications can arise in the placement and use of the implanted leador electrode.

Commercial off-the-shelf capacitor and inductor components are typicallynot comprised of biocompatible materials.

However, in accordance with the present invention, the inductor andcapacitor elements can be constructed to be completely biocompatible. Inthis case it would be not necessary to place them in a biocompatiblehermetic container. This would have great advantages in further reducingboth size and cost. In this regard, US 2009/0116167, published May 7,2009, and US 2009-0259265, published Oct. 15, 2009, are hereinincorporated by reference.

With reference to FIG. 14, it is a feature of the present invention thatcustom or “off-the-shelf” non-biocompatible miniature inductor 146 andcapacitor 148 components are mechanically installed in hermetic packagesor containers 156 in series, but have electrical circuit traces thatcouple the lumped inductor and capacitor elements electronically inparallel, thereby forming bandstop filters 128 as described above. FIG.14 illustrates an hermetically sealed container 156 having the inductor(L) and capacitor (C) components installed therein in series with oneanother, but whose lumped L and C elements are coupled electronically inparallel, so as to form one or more bandstop filters. The hermeticallysealed container 156 is very small in diameter or cross-section and canbe disposed between portions of an implantable lead 114, within anelectrode assembly, etc. FIG. 15 shows the exemplary hermetically sealedcontainer 156 adjacent to a United States penny or one-cent coin 158.

FIG. 16 is a cross-sectional view taken generally along line 16-16 ofFIG. 14 and shows the various component parts of the hermetically sealedcontainer 156. The container 156 comprises a housing 160 which isbiocompatible. By way of example, the housing 160 can be comprised of abiocompatible metal or alloy, such as titanium, platinum,platinum-iridium, gold, silver, etc., or a non-metallic material such assapphire, ruby, alumina, ceramic, etc. The inductor 146 and thecapacitor 148 are disposed on a substrate 162 and physically arranged inseries, or end-to-end, with one another yet conductively orelectronically coupled to one another in parallel. Circuit traces 164and 166 are conductively coupled to the inductor 146 and capacitor 148of the bandstop filter 128 and extend to conductive terminals 168 and170 of hermetic seal assemblies 172 and 174. The conductive terminals168 and 170 are designed to be conductively coupled to portions of theimplantable lead 114 or electrode assembly, and that any conductivemembers which can be conductively coupled to the bandstop filter 128within container 156 and extend therethrough in a hermetic fashion couldbe used.

FIG. 17 is an enlarged perspective view of the hermetic seal assembly174, having the terminal 170 extending therethrough to a crimp, solderjoint or laser weld tip 176. The electrical connection to the tip 176could also be formed by thermal-setting conductive adhesives. Theterminal 170 is attached to an insulator 178, which is in turn attachedto an outer ferrule 180.

FIG. 18 is a cross-section drawing taken along line 18-18 from FIG. 16.The terminal 170 is preferably of a common platinum-iridium alloy, suchas 9010 or 8020. However, any biocompatible and suitable material couldbe used in place of platinum-iridium. Gold braze 182 forms a hermeticseal between terminal 170 and insulator 178. The insulator 178 may be apolished sapphire, ruby, polycrystalline alumina, or even glass or ageneral ceramic material. Sputtering would first be deposited on thesurfaces so that the gold braze 182 will readily adhere and wet. Goldbraze 184 forms a hermetic seal between insulator 178 and the ferrule180. Gold brazes 182 and 184 are generally pure gold brazes forbiocompatibility and long term reliability. The surface preparationprocess for the ceramic insulator 178 can be as follows: C-Axis singlecrystal, polycrystalline alumina (A12O3), Zirconia Stabilized Aluminaand/or Yttria Tetragonal Zirconia Polycrystalline YTZP is etched usingRF plasma before PVD sputtering using a biologically compatible metallicsystem. Plasma cleaning removes organic surface contamination andhydroxyl/oxides resulting in a higher energy surface. This activatedsurface readily forms strong covalent bonds with metallization atomspromoting robust, hermetic adhesion. Through industry standard processrefinements, the resulting low stress, dense coating does not spall offor blister and improves the function and reliability of the final brazedjoint. The outer ferrule 180 is also, preferably, of platinum-iridiumsince it's very easy to laser weld. It is also radio-opaque.

In the preferred embodiment, the insulator 178 would be a polishedsapphire. It would then go through a plasma-etch process, such as a 500watt plasma-etch, to increase its surface roughness. Titanium lignummetallization would be a preferred sputter material for adhesion andwetting of the associated gold braze pre-forms.

In FIG. 17, one can see that the interior tip 176 of the terminals 168and 170 has been extruded to be fitted into an aperture, socket, etc. ofthe conductive substrate or circuit traces 164 and 166. Alternatively,the interior tip 176 may have an aperture therethrough so that a crimpedconnection can be formed between it and the conductive substrate orcircuit traces 164 and 166, and subsequently laser welded. The method ofattachment to the interior tip 176 will vary in accordance with the typeof attachment desired to the internal circuitry of the bandstop filter128. In any event, the conductive terminals 168 and 170 are conductivelycoupled to the bandstop filter 128 as the associated hermetic sealassemblies 172 and 174 are slid into place and hermetically sealed bylaser welding 186 to the housing 160 of the container 156.

FIG. 16 shows the bandstop filter 128 comprised of the inductor 146 andcapacitor 148, and the flexible circuit substrates 164 and 166 extendingtherefrom, attached to the terminals 168 and 170 so as to place theterminals 168 and 170 in electrical series with one another. However,the inductor 146 and the capacitor 148, although placed end-to-end andphysically in series with one another, are conductively coupledelectrically with one another in parallel. An insulating material 188,such as a thermal-setting non-conductive polymer, at least partiallyfills the remainder of the housing 160 to provide protection andmechanical robustness to the overall container assembly 156. Thisstructure lends itself to a novel “ship-in-the-bottle” method ofmanufacturing. That is, all of the elements contained within the housing160 are pre-assembled outside the housing. In particular, the terminal168, the substrate 162 containing the inductor 146 and capacitor 148,and the opposite terminal 170 and the associated hermetic seals 172 and174, are all pre-assembled outside of the overall housing 160. Thisfacilitates proper electrical connections and electrical testing of thepre-assembly. In addition, this entire subassembly can go through highreliability screening. Typically, this would consist of thermal cyclingor thermal shock followed by a burn-in, which means applying arelatively high voltage at elevated temperature to the circuitcomponents and then exhaustive electrical test afterwards. Once all ofthis has been done, this entire pre-assembly is slipped inside theoverall cylindrical housing 160 and then a final laser weld 186 isformed.

FIGS. 16 and 19 also show an optional conformal coating 190 which isprovided over the two gold brazes 182 and 184. This conformal coating190 could also be applied to the entire outer surface of the housing 160and a portion of terminals 168 and 170, as well as optionally over theelectrical attachments to the lead system. This conformal coating 190 isimportant to provide electrical isolation between the two terminals 168and 170. When directly exposed to body fluids (which containelectrolytes), gold can migrate in the presence of a voltage bias. Ithas been shown that pacemaker pacing pulses in saline solution canactually cause a gold electromigration or electroplating action. Theconcern is that the gold braze materials 182 and/or 184, under voltageor pulse bias, may over time migrate or deposit (electro-plate) ontoanother surface such as the terminal 170 or the housing 160, which couldnegatively affect the long-term hermeticity and reliability of thehermetic seal assembly 174. Accordingly, the conformal coating orbackfill 190 is placed as shown to cover both of the gold brazes 182 and184. The conformal coating 190 may comprise thermal-settingnon-conductive adhesives, silicones, parylene (which is vapordeposited), and the like, including epoxies, polyimides, polyethyleneoxide, polyurethane, silicone, polyesters, polycarbonate, polyethylene,polyvinyl chloride, polypropylene, methylacrylate, para-xylylene, andpolypyrrhol. In particular, Epo-tek H81 is considered a preferred epoxywhich has already been tested for long-term biocompatibility.

A complete conformal coating 190 over the entire housing 160 may bedesirable to provide electrical isolation between the conductiveterminal pins 168 and 170. This provides critical performance capabilityin the event of complete saturation of the housing 160 in saline orbiological fluid. See, for example, FIG. 45. Additional performancebenefits for a conformal coating 190 include lubricity, radiopacity, andwear resistance.

FIG. 20 illustrates a multi-layer flex cable 192 onto which the inductor146 and capacitor 148 are mounted. The inductor 146 is a chip inductorhaving first and second conductive termination surfaces 194 and 196which are spaced from one another in non-conductive relation. Thecapacitor 148 also has first and second conductive termination surfaces198 and 200 which are spaced apart from one another in non-conductiverelation. The chip inductor 146 can be any number of chip inductortypes, however the present invention is also not limited to chipinductors only. The inductor 146 could also be a solenoid inductor, atoroidal inductor, or any type of inductor that is known in the priorart. Moreover, the chip capacitor 148 can be any number of chipcapacitor types, but the present invention is not limited to chipcapacitors only. The capacitor 148 may be of many different types ofcapacitor technologies, including film capacitors, tantalum capacitors,monolithic ceramic capacitors, electrolytic capacitors, feedthrough-typecapacitors, or even tubular capacitors. FIG. 20 shows that the inductor146 and the capacitor 148 are physically disposed in series relative toone another, such that they are generally aligned with one another alonga common longitudinal axis and placed end-to-end. However, in accordancewith the present invention, the inductor 146 and the capacitor 148 areconductively or electrically coupled to one another in parallel. FIG. 22is an electrical schematic diagram of the bandstop filter of FIGS. 20and 21. When electrically connected as shown in FIG. 21, the secondconductive terminal 196 of the inductor 146 is spaced a suitabledistance away from the first conductive terminal 198 of the capacitor148. The reason that these termination surfaces 196 and 198 must beplaced apart is that in the presence of an MRI scanner, a substantial RFvoltage can be generated across this gap. Arching or even short circuitsmay undesirably occur. Another concern is that a long term failure mayoccur due to the formation of metal dendrites or whiskers. This canhappen even in the presence of a low voltage bias. However, having alarge physical gap between the termination surfaces 196 and 198 isgenerally undesirable because it increases the overall length of thebandstop filter 128. As previously mentioned, the most criticaldimension is the diameter. However, it is also important that theoverall assembly not get too long.

FIG. 20 may be compared with FIG. 16 to see alternative configurationsof the attachment between conductive terminals 168 and 170, and theconductive circuit traces or electrodes in 164 and 166. FIG. 16.illustrates a crimp configuration between the circuit traces orconductive substrates 164 and 166, and the respective tips 176 of theconductive terminals 168 and 170. In FIG. 20, an alternativeconfiguration is shown wherein the hermetic seal assemblies 172 and 174are pre-mounted to the conductive circuit traces or substrates 164 and166, and attached thereto by resistance welding or the like.

FIG. 23 illustrates an alternative embodiment wherein a flexible circuitsubstrate 202 is shown. For robotic manufacturing, it is highlydesirable if the circuit substrate 202 be laying flat while the pick andplace robots place the inductor 146 and the capacitor 148 components.The circuit substrate 202 includes portions which are conductive andother portions which are non-conductive, such that the conductiveportions or traces of the substrate 202 place the inductor 146 andcapacitor 148 in parallel electrical connection, although the inductor146 and capacitor 148 are disposed generally end-to-end physically inseries with one another. As illustrated in FIG. 24, the substrate 202 isthen folded up so that it will fit conveniently into the cylindricalhousing 160 as previously illustrated in FIG. 16.

FIG. 25 shows another arrangement for an inductor 146 and a capacitor148 physically disposed in series with one another in that they arearranged physically generally end-to-end, and yet the inductor 146 andthe capacitor 148 are electrically connected in parallel to form abandstop filter 128. A first conductive substrate or circuit trace 164conductively couples the first conductive terminals 194 and 198 of theinductor 146 and the capacitor 148. An insulator 204 prevents conductivecontact between the conductive substrate circuit trace 164 and thesecond conductive termination surface 196 of the inductor 146.Similarly, a conductive substrate or circuit trace 166 is conductivelycoupled to and extends between the second conductive termination surface196 of the inductor 146 and the second conductive termination surface200 of the capacitor 148. Another insulative layer 206 is disposedadjacent to the circuit trace or substrate 166 to prevent electricalcontact between the first conductive termination surface 198 of thecapacitor and the circuit trace or substrate 166. Conductive couplingcan be by any known means, including solders or brazes. An insulator orinsulating material is disposed between adjacent ends of the inductor146 and the capacitor 148 to prevent arching or short circuits fromdeveloping between the adjacent conductive termination surfaces in thepresence of, for example, an MRI scanner wherein a substantial RFvoltage can be generated across this gap. The physical/electricalschematic model for the embodiment shown in FIG. 25 is illustrated inFIG. 21.

FIG. 26 illustrates an alternative embodiment wherein the inductor 146and the capacitor 148 are disposed on generally opposite first andsecond surfaces of a non-conductive substrate 206. Nonetheless, theinductor 146 and the capacitor 148 are generally arranged end-to-end andin series with one another. They are merely placed on opposite sides ofthe non-conductive substrate 206. A conductive substrate or circuittrace 164′ extends from the first conductive terminal 198 of thecapacitor 148 and is conductively coupled to a circuit trace 164extending from the first conductive terminal 194 of the inductor 146 bymeans of a conductive connection through a passageway or through hole208 extending through the non-conductive substrate 206. Similarly, aconductive substrate or circuit trace 166′ extends from the secondconductive terminal 196 of the inductor 146 across the non-conductivesubstrate 206 and is placed in conductive relation with the secondconductive terminal 200 of the capacitor 148, such as by means of theconductive passage 210 which interconnects the circuit trace 166′ withthe circuit trace 166. The ends of circuit traces 164 and 166 can becoupled in series to the desired lead, electrode assembly, etc.

It will be appreciated that all of the assemblies illustrated in FIGS.20-41 may be placed within a hermetically sealed container or package156 so that off-the-shelf non-biocompatible inductor and capacitorcomponents may be used. As such, conductive substrates, circuit tracesor the like extending from the bandstop filter 128 will be conductivelycoupled to conductive contacts, such as terminals 168 and 170, extendingthrough the housing 160 of the hermetically sealed assembly. In thismanner, the hermetically sealed container 156 can be physically disposedin series between first and second portions of a lead or an electrode soas to place the bandstop filter 128 in series therewith.

FIGS. 27 and 28 are similar to FIGS. 20 and 21, but illustrate thepreferred manner of electrically attaching the inductor 146 and thecapacitor 148 in parallel while simultaneously arranging them physicallyin series, in accordance with the present invention. FIG. 27 differsfrom FIG. 20 in that the conductive circuit traces or substrates 164 and166 are shown with much of the insulative and overmolding material ofthe substrate or flex cable 192 (FIG. 20) removed. Notably, thearrangement of components illustrated in FIGS. 27 and 28 requires nospace between the inductor 146 and the capacitor 148, thus minimizingthe longitudinal dimensions of the bandstop filter 128.

As seen best in FIG. 27, the second termination surface 196 of theinductor 146 is electrically shorted or at the same potential as thefirst termination surface 198 of the capacitor 148. By having a zero ornearly zero potential, there is no chance that arching, shorting ordendritic growth between these opposed surfaces 196 and 198. This alsoeliminates a space or gap between the inductor 146 and the capacitor148. As shown in FIG. 27, a conductive bonding pad 214 is coupled to theconductive substrate 166 and conductively coupled to the secondconductive terminal 200 of the capacitor 148. An insulative layer 216extends between the circuit substrates 166 and 164. A conductive pad 218comes into contact with conductive terminals 196 and 198 of the inductor146 and the capacitor 148. Conductive passthroughs 220 extend from theconductive pad 218 through the insulative layer 216 and to theconductive circuit substrate 166 so as to place the conductive terminals196 and 198 in conductive relation with each other and with the circuittrace or substrate 164. Similarly, a non-conductive insulation layer 222extends between circuit substrates 164 and 166 and has a conductive pad224 on an upper surface thereof which communicates with a conductivethrough hole 226 to the conductive substrate 164, so as to place thefirst conductive terminal 194 of the inductor 146 in conductive relationand connection with the circuit substrate 166.

This arrangement is diagrammatically illustrated the physical/electricalschematic of FIG. 28, wherein the capacitor 148 and inductor 146 aredisposed physically in series with one another, but electrically andconductively coupled to one another in parallel. However, the entirebandstop filter, comprised of the capacitor 148 and the inductor 146 isin series with terminals T₁ and T₂, which could comprise the ends of theconductive substrates or circuit traces 164 and 166, the terminals 168and 170, etc., so as to place the overall assembly in series with theimplantable lead or electrode of a medical device. By carefully tracingeach circuit, one can see that the inductor 146 ends up in parallel withthe capacitor 148, forming a parallel resonant L-C bandstop filter 128,as illustrated in the electrical schematic drawing of FIG. 22.

There are particular challenges to designing and assembling componentsthis small. Placing them in a hermetic package is even more challenging.In the present invention, a pre-assembly or subassembly may comprise thecircuit traces, the inductor 146 and the capacitor 148 components, andthe electrical connections. Then the hermetic seal assemblies 172 and174 are attached to both ends of this rigid or flexible pre-assembly.This entire assembly is slid into a metallic tube or housing 160(typically platinum or titanium), and then relatively low energy laserwelds are used to make the final hermetic seal. The laser weldsgenerally involve a spot size of 0.005 inches, which limits the amountof heating that's involved. This guarantees that the sensitive internalelectrical connections and components will not be damaged.

FIGS. 29-31 illustrate a configuration where two bandstop filters 128and 128′ are placed in series. The first bandstop filter 128 consists ofcapacitor 148 and inductor 146. The second bandstop filter 128′ consistsof capacitor 248 and inductor 246. The first conductive substrate orcircuit trace 164 cooperates with an intermediate internal circuit traceor conductive substrate (not shown) to conductively couple the capacitor148 and the inductor 146 of the first bandstop filter 128 in parallelelectrical relation with one another, and the second end circuit traceor conductive substrate 166 cooperates with the intermediate circuittrace or conductive substrate to place the capacitor 248 and theinductor 246 of the second bandstop filter 128′ in parallel with oneanother such that the bandstop filters 128 and 128′ are placed in serieswith one another. One can follow the conductive circuit paths withinsubstrate 192 of each bandstop filter shown in FIG. 29, in thephysical/electric schematic illustration of FIG. 31.

In a preferred embodiment, the bandstop filters 128 and 128′ will beresonant at two different selective frequencies. For example, the firstbandstop filter 128 could have a self resonant frequency at 64 MHz whichcorresponds with a 1.5 Tesla MRI machine. The second bandstop filter128′ could be resonant at 128 MHz which is the RF pulsed frequency of a3 Tesla MRI system. Accordingly, by putting the two bandstop filters inseries, the bandstop filter network of FIG. 29 would offer a high degreeof attenuation to RF induced currents at both of these popular MRIfrequencies.

However, the bandstop filters 128 and 128′ can have the same resonantfrequency or approximately the same resonant frequencies. The advantageof having two bandstop filters in series with approximately the sameresonant frequency is that this increases the attenuation of the overallbandstop filter. By having the resonant frequencies of the bandstopfilters 128 and 128′ at slightly different frequencies, the resultantfilter has the advantage of broadening the 3 dB bandwidth (see FIG. 11).An advantage of the configuration shown in FIG. 29 is that theslenderness ratio of the assembly can be maintained. That is, theoverall diameter of the assembly must not be allowed to increase. Lengthis not nearly as critically important for an implantable lead, forexample, for cardiac rhythm application, as is diameter. Also currenthandling ability is very important. By having two bandstop filters inseries, one greatly increases the overall impedance and attenuation atresonance thereby providing a much higher level of protection toadjacent body tissues.

FIGS. 32-34 illustrate an alternative embodiment where three seriesinductors 146, 246 and 346 are placed in parallel with a singlecapacitor 148. It is well known in electrical engineering that wheninductors are wired in series they add up. In other words, the totalinductance is the sum of the three individual inductances. The threeinductors 146, 246 and 346, which are in series are together in parallelwith the capacitor 148, form the bandstop filter 128 as shown in FIG.34. This arrangement has particular advantages for AIMD leadapplications. This allows one to have a relatively high value ofinductance while at the same time keeping the diameter orcross-sectional area very small. A disadvantage of this arrangement isthat the resistive losses of the three inductors add up in series. Thismakes the bandstop filter Q a little lower, tends to widen its 3 dBbandwidth, but also reduces its attenuation. The current handlingability, such as during an automatic external defibrillation pulse, isalso slightly compromised by the added series resistance. Conversely thecurrent handling ability and/or the bandstop filter Q can be improved byusing a larger wire/trace/pathway diameter or width. The reduction oninductance per component, compared to an inductor with the same lengthutilizing a smaller wire/trace/pathway diameter or width, can becompensated by the increased number of inductors. Of course one willappreciate that the three series inductors can be replaced with twoinductors, four inductors or more, all wired in series and then placedin parallel with the capacitor 148 to form a bandstop filter 128 havingthe desired characteristics.

FIG. 35 is an exploded perspective view of the electrical subassembly ofFIG. 32. Here, one can see that it has the same circuit substrate 192that was shown in FIG. 32, which includes an insulative layer 228. Itwill be appreciated that much of the insulation forming a portion of thecircuit substrate 192 has been removed in FIG. 35 to better illustratethe electrical circuit traces or substrates which electrically connectthe three inductors 146, 246 and 346 in series, and place them allelectrically in parallel with the capacitor 148. In this regard, theconductive circuit trace or substrate 164 extends nearly the length ofthe entire subassembly so as to conductively couple two both the firsttermination surface 194 of the first inductor 146 and to the secondtermination surface 200 of the capacitor 148. This is accomplished byproviding a conductive pad 224 a atop an insulation layer 222 a, and aconductive passthrough 226 a. The first conductive termination surface194 of the first inductor 146 is conductively coupled to the conductivepad 224 a which, in turn, conductively couples said first terminationsurface 194 to the substrate 164. In like manner, the second terminationsurface 200 is positioned adjacent and conductively coupled to aconductive pad 224 e which sits atop an insulative layer 222 e. Theconductive pad 224 e is conductively coupled to the substrate 164through a conductive through-hole 226 d. In order to place the threeinductors 146, 246 and 246 electrically in series, two conductive pads224 b and 224 c are provided which are electrically isolated from theunderlying substrate 164 by insulative layers 222 b and 222 c. Thesecond termination surface 196 of the first inductor 146 rests atop andis conductively coupled to the conductive pad 224 b as is the firsttermination surface 294 of the second inductor 246. This arrangementconductively couples the second termination surface 196 of the firstinductor 146 to the first termination surface 294 of the second inductor246. Similarly, the second termination surface 296 of the secondinductor 246 rests atop a conductive pad 224 c and is conductivelycoupled thereto, as is the first termination surface 394 of the thirdinductor 346. This arrangement conductively couples the secondtermination surface 296 of the second inductor 246 to the firsttermination surface 394 of the third inductor 346. Finally, the secondconductive termination surface 396 of the third inductor 346 isconductively coupled to the first termination surface 198 of thecapacitor 148 by means of a conductive pad 224 d on which bothtermination surfaces rest and are conductively coupled thereto. Thisconductive pad 224 d is situated atop an insulative layer 222 d and isconductively coupled to the conductive circuit trace or substrate 166 bymeans of conductive through-holes or passageways 226 b and 226 c.

FIGS. 36 and 37 illustrate yet another arrangement contemplated by thepresent invention, wherein the three inductors 146, 246 and 346 areplaced in series with one another physically, but coupled conductivelywith one another in parallel. The capacitor 148 is also conductivelycoupled with the inductors 146, 246 and 346 in parallel to create abandstop filter 128.

FIGS. 38 and 39 illustrate another arrangement contemplated by thepresent invention, wherein two capacitors 148 and 248 are placed inseries with one another physically but coupled conductively with oneanother in parallel. The capacitors are also conductively coupled withthe inductor 146 in series to create a bandstop filter 128. Yet anotheralternative is illustrated in FIGS. 40 and 41, wherein the capacitors148 and 248 are disposed physically in series with one another andconductively coupled to one another in series, yet conductively coupledto the inductor L in parallel to form a bandstop filter 128. In both ofthese latter two embodiments, the capacitors 148 and 248 and theinductor 146 are placed end-to-end and generally disposed in series withone another yet still form a bandstop filter without increasing theoverall diameter of the assembly. Thus, it will be appreciated thatdifferent values of the bandstop filter 128 may be obtained by placingmultiple capacitors or inductors physically in series with one another,but in various combinations of electrical and parallel coupling toachieve the desired values.

With reference now to FIG. 42, a passive electrode 230 typically used incardiac pacemaker applications is shown in which the hermetically sealedbandstop filter assembly of the present invention can be incorporated.FIG. 43 illustrates an active fixation Tip electrode 130 having a helixscrew 134 selectively extendable and retractable from the lead housing132. The helix screw 134 is retracted while the lead housing 132 isinserted endocardially to the correct location, for example, into theright ventricle. The physician then uses a tool (not shown) in thepectoral pocket and twists this entire assembly which literally screwsthe distal helix screw 134 into the myocardial tissue.

FIG. 44 is a cross-section taken along line 44-44 from FIG. 43. Shown isthe hermetically sealed bandstop filter assembly 156 that is embeddedwithin the overall lead housing 132. The hermetically sealed bandstopfilter assembly 156 can be as the assembly illustrated in FIGS. 14 and16, or any of the other variations illustrated herein or contemplated bythe present invention. The important aspect is that the various inductorand capacitor components be physically disposed in series relative toone another, yet conductively coupled in parallel to form one or morebandstop filters which are hermetically sealed in a biocompatiblecontainer for insertion into the electrode or leadwire of the medicaldevice.

FIGS. 45-47 illustrate a configuration where a chip inductor 146 isphysically disposed in series with a feedthrough capacitor 148, and yetis electrically connected in parallel to form a bandstop filter 128. Thechip inductor 146 and the feedthrough capacitor 148 are disposed withina hermetic container 156 comprising a housing 160 of a biocompatiblematerial which includes one open end, and a hermetic seal assembly 174disposed within the open end of the housing 160. The conductive terminal168 is conductively coupled to the housing 160 by a laser weld 232. Thefirst conductive termination surface 194 of the inductor 146 isconductively coupled to the housing 160 by means of a conductiveadhesive 234 or the like. The second conductive termination surface 196of the inductor 146 is similarly conductively coupled by means of aconductive adhesive 234 or the like, to a conductive bracket 236 whichis also conductively coupled to an extension 238 of the conductiveterminal 170 which extends through a central passageway of thefeedthrough capacitor 148. The first conductive termination surface 198of the capacitor 148 is conductively coupled to the housing 160 by meansof conductive adhesive 234 or the like, and the second conductivetermination surface 200 of the feedthrough capacitor 148 is conductivelycoupled to the extension 238 of the conductive terminal 170 by means ofconductive adhesive 234 or the like. The hermetic seal assembly 174disposed within the opening to the housing 160, and which preventsdirect contact between body fluids and the inductor 146, the capacitor148 and related electrical components, is essentially the same as thehermetic seal assembly 174 illustrated in FIGS. 16-19. The illustratedstructure advantageously eliminates one hermetic seal assembly incomparison with previously illustrated embodiments, by providing aterminal 168 which is shorted to the housing 160. As shown, theconformal coating 190 is applied over the entire outer surface of thehousing 160 as well as a portion of the terminals 168 and 170. Thisconformal coating 190 advantageously provides additional electricalisolation between the two terminals 168 and 170.

Accordingly, from all of the foregoing it will be appreciated that thepresent invention relates to passive bandstop filter circuits whereinone or more of both inductor 146 and capacitor 148 elements arephysically disposed in series but whose equivalent (lumped) L-Cparameters are electrically connected in parallel. The disclosedembodiments are particularly suitable for applications where it isimportant to keep the diameter or cross-sectional area of the bandstopfilter 128 relatively small as, for example, in medical implanted leads.Providing bandstop filters in such medical implanted leads serves toreduce the amount of radio frequency (RF) current associated heating dueto energy deposited on the leads during medical diagnostic procedures,such as magnetic resonance imaging (MRI). The bandstop filter 128 may bedesigned to be resonant at the MRI RF pulsed frequency and therebypresent a high impedance in the lead thus reducing RF current flow.

Although several embodiments have been described in detail for purposesof illustration, various modifications may be made without departingfrom the scope and spirit of the invention. Accordingly, the inventionis not to be limited, except as by the appended claims.

1. A lead wire system for use with an active implantable medical device,the lead wire system comprising: a) an implantable lead comprising atleast one lead wire having a length extending to and meeting with aproximal lead end and a distal lead end; b) a bandstop filter connectedin series with the lead wire somewhere along the length thereof, thebandstop filter comprising a capacitor segment having a capacitorsegment first end and a capacitor segment second end, and an inductorsegment having an inductor segment first end and an inductor segmentsecond end, wherein the capacitor segment first end is electricallyconductively connected to the inductor segment first end, and thecapacitor segment second end is electrically conductively connected tothe inductor segment second end so that the inductor and the capacitorare electrically coupled to one another in parallel; c) wherein thebandstop filter is electrically connected in series with the lead wiresomewhere along the length thereof with one of the capacitor and theinductor residing at a proximal location along the length of the leadwire with respect to the other of the capacitor and the inductorresiding at a distal location along the length; and d) wherein theinductor segment has an inductor segment inductance and an inductorsegment resistance, and the capacitor segment has a capacitor segmentcapacitance and a capacitor segment resistance.
 2. The lead wire systemof claim 1 wherein a Q of the bandstop filter is reduced by eitherreducing the Q of the inductor segment inductance, reducing the Q of thecapacitor segment capacitance, or both.
 3. The lead wire system of claim1 wherein the capacitor segment resistance is raised in order to reducethe Q of the capacitor segment.
 4. The lead wire system of claim 1wherein the Q of the bandstop filter circuit is reduced by increasingthe capacitor segment resistance.
 5. The lead wire system of claim 1wherein a Q of the bandstop filter is such that its 3 db bandwidthprovides attenuation across a range of MRI radio frequency (RF) pulsefrequencies.
 6. The lead wire system of claim 1 wherein the bandstopfilter is disposed at, proximate to or within a distal end of the leadwire.
 7. The lead wire system of claim 1 wherein the inductor segmentdoes not comprise ferritic, ferrite or ferro-magnetic core materials. 8.The lead wire system of claim 1 wherein the capacitor segment comprisesa ceramic capacitor.
 9. The lead wire system of claim 1 wherein the leadwire has a wire structure selected from the group consisting of aspiral, coaxial, filer, bifilar and multifilar wire structure.
 10. Thelead wire system of claim 1 wherein the bandstop filter isbiocompatible.
 11. The lead wire system of claim 1 wherein the inductorsegment is comprised of at least two series discrete inductors.
 12. Thelead wire system of claim 1 wherein the medical device is selected fromthe group consisting of a cochlear implant, a piezoelectric sound bridgetransducer, a neurostimulator, a brain stimulator, a cardiac pacemaker,a ventricular assist device, an artificial heart, a drug pump, a bonegrowth stimulator, a bone fusion stimulator, a urinary incontinencedevice, a pain relief spinal cord stimulator, an anti-tremor stimulator,a gastric stimulator, an implantable cardioverter defibrillator, a pHprobe, a congestive heart failure device, a pill camera, aneuromodulator, a cardiovascular stent, and an orthopedic implant. 13.The lead wire system of claim 1 wherein the inductor segment resistance,the inductor segment inductance, the capacitor segment capacitance, andthe capacitor segment resistance result in a Q of the bandstop filterhaving a 3 db bandwidth on the order of megahertz.
 14. The lead wiresystem of claim 13 wherein the 3 db bandwidth is tuned to a resonantcenter frequency as an MRI pulsed RF frequency.
 15. The lead wire systemof claim 1 wherein the bandstop filter is housed within a hermeticallysealed biocompatible container.
 16. The lead wire system of claim 15wherein a ceramic insulator material is hermetically sealed between aferrule and a terminal for the biocompatible container.
 17. The leadwire system of claim 15 wherein the biocompatible container is providedwith a conformal coating of a material selected from the groupconsisting of thermal-setting non-conductive adhesives, parylene,epoxies, polyimides, polyethylene oxide, polyurethane, silicone,polyesters, polycarbonate, polyethylene, polyvinyl chloride,polypropylene, methylacrylate, para-xylylene, and polypyrrhol.
 18. Thelead wire system of claim 1 wherein a cross section of the bandstopfilter perpendicular to the length is 6 French, or less.
 19. A lead wiresystem, which comprises: a) at least one lead wire having lengthextending to and meeting with a proximal lead end and a distal lead end;b) a bandstop filter connected in series with the lead wire andcomprising a capacitor segment having a capacitor segment first end anda capacitor segment second end, and an inductor segment having aninductor segment first end and an inductor segment second end, whereinthe capacitor segment first end is electrically conductively connectedto the inductor segment first end, and the capacitor segment second endis electrically conductively connected to the inductor segment secondend so that the inductor and the capacitor are electrically coupled toone another in parallel; and c) wherein the bandstop filter iselectrically connected in series with the lead wire somewhere along thelength thereof with one of the capacitor and the inductor residing at aproximal location along the length of the lead wire with respect to theother of the capacitor and the inductor residing at a distal locationalong the length.
 20. An active implantable medical device lead wiresystem, which comprises: a) an implantable lead comprising at least onelead wire having a length extending to and meeting with a proximal leadend and a distal lead end; b) a bandstop filter connected to the leadwire and comprising a capacitor segment having a capacitor segment firstend and a capacitor segment second end, and an inductor segment havingan inductor segment first end and an inductor segment second end,wherein the capacitor segment first end is electrically conductivelyconnected to the inductor segment first end, and the capacitor segmentsecond end is electrically conductively connected to the inductorsegment second end so that the inductor and the capacitor areelectrically coupled to one another in parallel; c) wherein the bandstopfilter is electrically connected in series with the lead wire somewherealong the length thereof with one of the capacitor and the inductorresiding at a proximal location along the length of the lead wire withrespect to the other of the capacitor and the inductor residing at adistal location along the length; d) wherein the inductor segment has aninductor segment inductance and an inductor segment resistance, and thecapacitor segment has a capacitor segment capacitance and a capacitorsegment resistance; and e) wherein the capacitor segment first end andthe inductor segment first end are electrically conductively connectableto an external portion of a terminal pin of a hermetic seal, and thecapacitor segment second end and the inductor segment second end are atthe proximal end of the lead wire.